When drilling oil and/or gas wells, oil-based drilling fluids are often used to cool the drill bit, remove rock chips, and control subsurface fluids. After being used, this fluid, known as drilling mud, contains undesirable solids. Before the mud can be used again, the solids must be removed.
Various devices are used to remove solids from drilling fluid. Large solids are often removed by passing the fluid through a vibrating porous membrane, or screen, and segregating the solids that are too large to pass through the screen. Centrifugal force may be used to remove finer solids from the drilling mud. However, ultra fine solids, i.e. those solids that are not removed from the fluid by mechanical means, such as vibratory separators and centrifuges, remain in the oil-based mud even after this processing. Continual re-use of the drilling fluid increases the amount of ultra fine solid contaminants present in the fluid.
These solids can affect many fluid system properties adversely. Formation clays are unavoidably incorporated into the fluid system, and depending on their nature and amount, the clay minerals can be beneficial or harmful to the fluid system. Contaminants, such as gypsum, can “cut” the fluid system causing particles to flocculate and the viscosity to increase. When this occurs, there is danger of torquing the drill pipe to the point of breakage or of causing a blowout. At high temperatures, gelation or thickening of the fluid can occur, leading to greatly increased pressure on the recirculation pump.
It would be an improvement to the art to be able to remove ultra fine solid contaminants from oil-based drilling fluid so that additional use of the drilling fluid is possible. One way to do this is through electrophoresis.
The application of an electric field to a solution will result in the migration of certain molecules in a particular direction. Positively charged molecules will migrate toward a negatively charged cathode while negatively charged molecules will migrate toward the positively charged anode. This process, known as electrophoresis, may be used to purify certain solutions.
Many electrophoresis devices include a positively charged electrode and a negatively charged electrode that are placed into a bath of solution, which is purified in a batch. Used drilling fluid may be treated in batches or continuously as the drilling operation progresses. Thus, it would be an improvement in the art to have an apparatus that provides continual ultra fine solids removal capability to a stream of such contaminated fluid. Such an apparatus can be used in series with other treatment apparatuses to remove contaminants from a stream of drilling fluid. It would also be an improvement to have an apparatus that can also remove ultra fine solids from a batch or store of drilling fluid.
While some electrophoresis devices include a scrubber for removing unwanted deposits on the anode, there is still a need for removing the contaminants that accumulate on the negatively charged cathode during a continuous treatment process.